1. Field of the Invention
The present invention relates to a new mold release composition for the production of molded articles based on polyurethanes or polyureas with selfreleasing properties, a mixture of compounds carrying isocyanate reactive groups containing this composition, a process for the production of elastic molded bodies with a compact surface layer using these mixtures, and the molded bodies obtained by this process.
2. Description of the Prior Art
The production of elastomeric molded articles based on polyurethanes or polyureas by the reaction inside closed molds of reaction mixtures composed of a polyisocyanate component, relatively high molecular weight compounds containing isocyanate reactive groups, low molecular weight chain lengthening agents and the usual auxiliary agents and additives has already been disclosed, for example in DE-AS No. 2,622,951 or in EP-B-No. 0,081,701. In these prior art processes, the reaction mixtures are generally prepared by the reaction injection molding technique and introduced into a mold as soon as they have been prepared. The resulting molded articles are then generally removed after a very brief dwell time in the mold. For satisfactory performance of this process it is essential that the molded articles should be easily released from the mold, especially if they are produced on a large scale. Not only the use of so-called "external mold release agents", i.e. mold release compositions with which the mold is coated before it is filled, but also the use of so-called "internal mold release agents" is very important for this purpose. "Internal mold release agents" are substances which are incorporated in the reaction mixture so that the molded product obtained adheres less firmly to the surface of the mold than it would if it did not contain such mold release agents. For the production of elastomeric molded products, in particular those having a density of about 0.8 to 1.4 g/cm.sup.3, it has been found very suitable to use combinations of zinc salts of long chained carboxylic acids, in particular zinc stearate, and certain organic compounds containing tertiary amine nitrogen atoms. One example of a typical compound of this kind containing tertiary amine nitrogen atoms is the addition product of about 5 mol of propylene oxide to 1 mol of ethylene diamine. These compounds containing tertiary amine nitrogen atoms act as solvents for the zinc salt which is generally difficult to dissolve and at the same time they impart a certain solubility to zinc stearate in mixtures of isocyanate reactive compounds which serve as the reaction partners for the polyisocyanates. Such mold release compositions and their use for the production of elastomeric molded articles have already been described, for example in U.S. Pat. Nos. 4,519,965, 4,581,386 and 4,585,803.
One disadvantage of these prior art mold release compositions, however, is that they have only a limited solubilizing effect so that when such prior art mold release compositions are added to mixtures of compounds containing isocyanate reactive groups of the kind used in the aforesaid process, the mixtures must be rapidly processed after addition of the mold release composition because the mold release effect diminishes if the mixtures are left to stand. In practice, therefore, the mold release compositions are generally added to the compounds containing isocyanate reactive groups only shortly before production of the molded articles. This incidentally also applies to mold release compositions consisting of zinc salts, in particular zinc stearate, and compounds containing primary amino groups of the kind recommended, for example in EP-A-No. 0,119,471.
It is an object of the present invention to provide new mold release compositions which do not have the above-described disadvantage of losing their mold release effect when stored in the form of mixtures ready for use.
This problem was able to be solved by means of the mold release compositions according to the invention described below. These mold release compositions contain certain selected tertiary amines of the kind described below as solvents or compatibility transmitting agents for the zinc salt, in particular zinc stearate. The mold release compositions according to the invention are distinguished in particular by a combination of the following advantages:
1. The mold release effect obtainable with the new mold release compositions is at least equal to the mold release effect obtainable with the mold release compositions known in the art.
2. Mixtures of compounds containing isocyanate reactive groups of the kind used for the production of elastomeric molded articles and containing mold release compositions according to the invention need not be processed immediately after they have been prepared (by adding the mold release composition to the other components) since molded products with excellent self-releasing properties can be obtained from the completely prepared mixtures regardless of whether or not the mixtures have been kept in storage before being molded. In practice, this means that the manufacturer of molded articles need no longer prepare the complete mixture freshly at frequent intervals by mixing the mold release composition with other compounds.